I know I cannot run the drain from a utility/laundry sink into the drain/vent for my bathroom sink but can I do the reverse? Run my bathroom sink drain into the drain/vent of my utility/laundry sink? Reason for asking... My shop will be on a small septic tank. My bathroom sink does not have a dedicated drain so I plan to wet vent it. It's between a toilet and a utility sink that will be outside of the bathroom. If it wet vents into the toilet it will obviously go to the septic. If I can wet vent it to the utility sink then I can run it out as gray water.